In a communication network including a plurality of transceivers, it may be necessary or at least desirable for a first transceiver, which has a synchronous communication link with a second transceiver, to be powered down and then powered back up again before there has been any significant frequency drift between the two transceivers. Before data transmission can recommence, the optimal sampling phase must be recovered at the first transceiver. As is known, the purpose of recovering the “sampling phase” is so that the correct time within a data symbol for which to take a sample can be determined (as compared with recovering the “sampling frequency” which involves estimating the symbol period so that samples can be taken at the correct rate). The receiver process of recovering (locking) both the sampling phase and the sampling frequency is cumulatively referred to as “timing recovery.”
An example of this power down/power up scenario may arise in the current scheme for Energy-Efficient Ethernet proposed by the Institute of Electrical and Electronics Engineers (IEEE), i.e., IEEE P802.3az Energy-Efficient Ethernet Study Group. The main purpose of the IEEE scheme is to develop a standard to make Ethernet connections more energy (power) efficient. Such a scheme could help to reduce energy consumption in servers, personal computers, and laptops, as well as in switches, routers and other network equipment. In the IEEE scheme, it is proposed that when the medium access controllers (MACs) at both ends of an active Ethernet link have no data to send, then one or both transceivers could be powered down to save power. The transceivers would then have to wake rapidly should any data arrive to be transmitted so that the link would not be lost.